The XPA Messaging System

The XPA messaging system provides seamless communication between many
kinds of Unix programs, including X programs and Tcl/Tk programs. It
also provides an easy way for users to communicate with these
XPA-enabled programs by executing XPA client commands in the shell or
by utilizing such commands in scripts. Because XPA works both at the
programming level and the shell level, it is a powerful tool for
unifying any analysis environment: users and programmers have great
flexibility in choosing the best level or levels at which to access
XPA services, and client access can be extended or modified easily at
any time.

A program becomes an XPA-enabled server by defining named points of
public access through which data and commands can be exchanged with
other client programs (and users). Using standard TCP sockets as a
transport mechanism, XPA supports both single-point and broadcast
messaging to and from these servers. It supports direct communication
between XPA clients and servers, or indirect communication via an
intermediate message bus emulation program. Host-based access control
is implemented, as is as the ability to communicate with XPA servers
across a network.

Because XPA consists of a library and a set of user programs, it is
most appropriately built from source. XPA has been ported to Solaris,
Linux, Mac OSX (darwin) and Windows 98/NT/2000/XP. Once the source
code tar file is retrieved, XPA can be built and installed easily
using standard commands: